Initial Soil Water Research Articles

Pesticides trapping performance of vegetative filter strips in black soil region, Northeast China: controlled experiments and VFSMOD-W modeling

The Northeast black soil region in China is an important grain-producing area where various pesticides are extensively used to increase grain yields. However, this practice poses serious risks to the ecological health of soil and water systems, necessitating effective measures. Vegetative filter strips (VFS) are commonly used to mitigate agricultural diffuse pollutants, but their efficiency varies across different regions, requiring assessment. This study employed flume experiments, the VFSMOD-W model, and redundancy analysis (RDA) to evaluate the efficacy of VFS in runoff, sediment, and pesticide removal, as well as influencing factors. The results showed that VFS reduced outflow rate of runoff by 8 %–64 % and sediment by approximately 90 %, achieving load removal rates of 61 % and 95 % respectively. Pesticide load removal efficiency ranged from 37 % to 94 %, with higher efficiency for adsorbed pesticides like chlorpyrifos compared to water-soluble ones like atrazine. Interflow and vertical seepage were significant pathways for pesticide transport in VFS, with chlorpyrifos concentrations at 4 %–26 % and atrazine at 20 %–37 % of inflow concentrations. The VFSMOD-W model accurately predicted VFS efficiency (NSE > 0.90), and RDA results indicated that environmental factors could explain 86.7 % of the variation in VFS performance, with soil vertical saturated hydraulic conductivity (VKS) being the most influential factor, followed by rainfall intensity (T), saturated soil water content (OS), initial soil water content (OI), and filter slope for each segment (SOA). Optimizing soil moisture characteristic factors and increasing infiltration are crucial for VFS performance. Applying VFSMOD-W for precise VFS design can help reduce construction costs. In the future, long-term field monitoring and evaluation of VFS efficiency after implementation should be conducted in the black soil region of Northeast China to provide data supporting the improvement of VFSMOD-W simulation accuracy. This will also offer recommendations for the government in formulating VFS configuration schemes.

Estimating aboveground biomass dynamics of wheat at small spatial scale by integrating crop growth and radiative transfer models with satellite remote sensing data

Aboveground biomass (AGB) of plants is an agroecological indicator that can be used to monitor crop growth status and quantify biomass carbon stock in agricultural ecosystems. Although satellite remote sensing data and crop models are widely employed to estimate AGB dynamics, their application in small-scale research plots is often constrained by the unavailability of freely and timely high-resolution satellite imageries and the challenge of acquiring reliable model inputs like initial soil water and nitrogen content. This study integrated a crop growth model (APSIM-Wheat) and radiative transfer model (PROSAIL) to estimate AGB dynamics at a small plot scale (ca. 5 to 20 m2) within variety trials (ca. 1 to 2 ha) by assimilating trial-level remote sensing data into the hybrid APSIM-PROSAIL model. The APSIM-PROSAIL integration, developed by deriving PROSAIL input parameters from APSIM-Wheat output variables, was verified by evaluating its capacity to reproduce trial-level Sentinel-2 (S2) NDVI dynamics across 30 variety trials in 2020. The comparison of the simulated and observed trial-level S2 NDVI dynamics yielded an overall RRMSE of 18.2% (n = 646 observations), suggesting the potential of using observed S2 NDVI dynamics to constrain APSIM-PROSAIL and estimate environment variables in cropping systems. This constraint was subsequently assessed in 28 variety trials in 2021, where APSIM-PROSAIL inversely estimated unknown trial-specific variables including initial soil water and nitrogen content across the trials. Using the estimated initial soil status and the plot information including genotypes and management as sown, we demonstrated that this method could also facilitate accurate retrievals of plot-level AGB dynamics with an overall RRMSE of 20.9% (n = 976 measurements). The proposed APSIM-PROSAIL demonstrated the capability to accurately retrieve plot-level AGB dynamics and reproduce trial-level S2 NDVI dynamics across a broad and diverse range of variety trials in the Australian Wheatbelt, indicating its potential utility to facilitate biomass carbon stock assessment. It holds the potential as a tool to explore the relationships between canopy spectral information and crop traits in response to genotype-environment-management interactions in agricultural ecosystems. The method enables the examinations of within-field variabilities for crop traits through retrieving them at small spatial scales from coarse remote sensing data.

Migration Rules and Mechanisms of Nano-Biochar in Soil Columns under Various Transport Conditions.

Compared to traditional biochar (BC), nano-biochar (NBC) boasts superior physicochemical properties, promising extensive applications in agriculture, ecological environments, and beyond. Due to its strong adsorption and migration properties, NBC may carry nutrients or pollutants to deeper soil layers or even groundwater, causing serious environmental risks. Nevertheless, the migration rules and mechanisms of NBC in soil are still unclear. Therefore, this study employed soil column migration experiments to systematically explore the migration rules and mechanisms of NBC under various flow rates, initial soil water contents, soil depths, and soil textures. The results showed that regulated by smaller particle size differences and greater surface charges, NBC exhibited a stronger migration ability compared with traditional BC. As the soil texture transitioned from fine to coarse, the migration capability of NBC significantly improved, driven by both pore structure and interaction forces as described by the DLVO theory. The migration ability of NBC was also greatly boosted as the soil transitioned from saturated to unsaturated conditions, primarily because of preferential flow. When the flow rate increased from 70% KS to 100% KS and 130% KS, the migration ability of NBC also increased accordingly, as changes in injection flow rates altered the velocity distribution of pore water. NBC in 25 cm soil columns was more prone to shallow retention compared with 10 cm soil columns, resulting in weaker overall migration ability. In addition, through fitting of the two-site kinetic model and related parameters, the penetration curves of NBC under various variable conditions were effectively characterized. These findings could offer valuable insights for NBC's future efficient, rational, and sustainable utilization, facilitating the evaluation and mitigation of its potential environmental risks.

Light thinning effectively improves forest soil water replenishment in water-limited areas: Observational evidence from Robinia pseudoacacia plantations on the Loess Plateau, China

Soil water plays a key role in vegetation growth and recovery, mainly replenished by rainfall in the water-limited areas. Thinning is an important practice for forest reconstruction and soil water regulation. However, the effects of different thinning intensities on the dynamics of soil water and its replenishment by rainfall have been inadequately quantified, which could provide a guide for reasonable thinning intensity determination for in high-density forests from a hydrological perspective. In this study, one nonthinning plot and 5 plots with different thinning intensities, i.e., 35 % (light), 45 % (medium), 55 % (moderate), 65 % (heavy) and 80 % (extremely heavy) in Robinia pseudoacacia plantations, which are widely planted on the Loess Plateau, were set up. The volumetric soil water content (SWC) at 0–200 cm depths and rainfall were observed simultaneously and continuously for up to two years. The soil properties and vegetation structure in each plot were also measured regularly. The results showed that (1) the SWC in all the thinning plots was significantly greater than that in the nonthining plot (P < 0.05). (2) The replenishment increased with increasing thinning intensity, and then decreased after reaching a maximum at T35 % under most rainfall events except for light events. (3) The variations in the soil water response characteristics among the plots with different thinning intensities were mainly significantly correlated with the initial soil water content (ISWC), leaf area index (LAI) and understorey vegetation characteristics (P < 0.05). (4) Based on the relationship between soil water replenishment and retention with thinning intensity and stand density, quantitative equations were fitted to determine the reasonable thinning intensity (22–28 %) and retained stand density (1019–1091 trees/ha), respectively. Our study concluded that thinning could effectively improve soil water, especially light thinning, which could obviously enhance the replenishment of soil water by rainfall in Robinia pseudoacacia plantations. This study can provide a reference for determining forest thinning intensity or stand retention density, which is beneficial for water and reforestation management in water-limited regions.

Achieving stable and sustainable Mungbean yields in Australia via optimal sowing dates

ContextAs a rainfed, short-season crop, mungbean is a particularly attractive summer rotation option for Australian farmers, but the rate of mungbean adoption in Australia is low due to its high yield instability. A lack of research conducted on modern mungbean in Australia has hindered farmers’ ability to understand how to best manage the crop and close the yield gap. ObjectivesThe aim of this study was to provide recommendations for optimal sowing windows (balancing maximum yield potential with minimum risk—i.e. instability and crop failure). MethodsWe simulated 60 years of growing mungbean at 180 different sowing times, four different initial soil water levels and at seven sites across Queensland and New South Wales using the new Agricultural Production Systems sIMulator Next Generation (APSIM NextGen) Mungbean model. We then calculated the impact of sowing date on mungbean water use efficiency and on the soil water deficit for the subsequent crop in the rotation. ResultsHigher initial soil water levels decreased risk (instability and failure) at all sites. Arid sites with high evaporative demand had optimal sowing windows later (February) in the growing season. More temperate sites yielded better with higher levels of stability when sown between November and January. Sowing in September/October is not recommended in any site as it coincided with low yield stability and water use efficiency. Not all sites had a clear optimal sowing window. We conclude, therefore, that in some environments, sowing time can only marginally reduce risks in growing mungbean. ConclusionsWe identified optimal sowing window that can reduce risks of a failed crop by 20 % and increase stability without losing yield potential. The timing of the optimal sowing window for a given site appears to be influenced by avoiding periods with high evaporative demand during the reproductive phase. ImplicationsModelling has been critical for exploring the trade-offs between maximizing and stabilizing mungbean yields over a wide range of environments and growing seasons to determine the optimal sowing windows across the main growing environments in Australia.

Impacts of Climate Change and Adaptation Strategies for Rainfed Barley Production in the Almería Province, Spain

Mediterranean water-stressed areas face significant challenges from higher temperatures and increasingly severe droughts. We assess the effect of climate change on rainfed barley production in the aridity-prone province of Almería, Spain, using the FAO AquaCrop model. We focus on rainfed barley growth by the mid-century (2041–2070) and end-century (2071–2100) time periods, using three Shared Socio-economic Pathway (SSP)-based scenarios: SSP1-2.6, SSP2-4.5, and SSP5-8.5. Using the paired t-test, Spearman and Pearson correlation coefficient, Root Mean Squared Error, and relative Root Mean Squared Error, we verified AquaCrop’s ability to capture local multi-year trends (9 or more years) using standard barley crop parameters, without local recalibration. Starting with a reference Initial Soil Water Content (ISWC), different soil water contents within barley rooting depth were modelled to account for decreases in soil water availability. We then evaluated the efficiency of different climate adaptation strategies: irrigation, mulching, and changing sowing dates. We show average yield changes of +14% to −44.8% (mid-century) and +12% to −55.1% (end-century), with ISWC being the main factor determining yields. Irrigation increases yields by 21.1%, utilizing just 3% of Almería’s superficial water resources. Mulches improve irrigated yield performances by 6.9% while reducing irrigation needs by 40%. Changing sowing dates does not consistently improve yields. We demonstrate that regardless of the scenario used, climate adaptation of field barley production in Almería should prioritize limiting soil water loss by combining irrigation with mulching. This would enable farmers in Almería’s northern communities to maintain their livelihoods, reducing the province’s reliance on horticulture while continuing to contribute to food security goals.

Statistical sampling of missing environmental variables improves biophysical genomic prediction in wheat.

The integration of genomic prediction with crop growth models enabled the estimation of missing environmental variables which improved the prediction accuracy of grain yield. Since the invention of whole-genome prediction (WGP) more than two decades ago, breeding programmes have established extensive reference populations that are cultivated under diverse environmental conditions. The introduction of the CGM-WGP model, which integrates crop growth models (CGM) with WGP, has expanded the applications of WGP to the prediction of unphenotyped traits in untested environments, including future climates. However, CGMs require multiple seasonal environmental records, unlike WGP, which makes CGM-WGP less accurate when applied to historical reference populations that lack crucial environmental inputs. Here, we investigated the ability of CGM-WGP to approximate missing environmental variables to improve prediction accuracy. Two environmental variables in a wheat CGM, initial soil water content (InitlSoilWCont) and initial nitrate profile, were sampled from different normal distributions separately or jointly in each iteration within the CGM-WGP algorithm. Our results showed that sampling InitlSoilWCont alone gave the best results and improved the prediction accuracy of grain number by 0.07, yield by 0.06 and protein content by 0.03. When using the sampled InitlSoilWCont values as an input for the traditional CGM, the average narrow-sense heritability of the genotype-specific parameters (GSPs) improved by 0.05, with GNSlope, PreAnthRes, and VernSen showing the greatest improvements. Moreover, the root mean square of errors for grain number and yield was reduced by about 7% for CGM and 31% for CGM-WGP when using the sampled InitlSoilWCont values. Our results demonstrate the advantage of sampling missing environmental variables in CGM-WGP to improve prediction accuracy and increase the size of the reference population by enabling the utilisation of historical data that are missing environmental records.

Grass cover and shallow tillage inter-row soil cultivation affecting CO2 and N2O emissions in a sloping vineyard in upland Balaton, Hungary

Greenhouse gas (GHG) emissions can accelerate the current climate change trend, resulting in higher soil temperatures and changes in soil water contents. The aim of the study was to investigate to what extent different cultivation methods and sampling positions on the slope (location along the slope) are affecting soil GHG emissions in vineyards. In the study, different inter-row soil cultivation methods were investigated including shallow soil tillage (ST) and grass cover (GC) inter-rows. Intact soil columns were collected and different soil water contents were applied under a laboratory environment to simulate different precipitation conditions. Our findings showed significant differences in the emitted CO2 and N2O between the cultivation methods, where the GC soil had 2.9 times higher average CO2 and 6.1 times higher N2O emissions compared to the bare, ST soil. The amount of initial and longer term soil water content significantly influenced soil-derived GHG emissions, with the highest averaged values observed for the continuously high water content soil samples (0.377 mgCO2 m−2 s−1 and 0.076 μgN2O m−2 s−1). For the GC inter-rows, we also observed significant differences in the GHG emissions among the different sampling positions of the investigated slopes. We found that besides the different soil water contents, the main causes for these differences could be the variances in the soil physical and chemical properties. The findings of this study can be used to better estimate soil GHG emissions at various water contents, for different inter-row soil management cultivation methods, and potentially mitigate some adverse effects of global warming by reducing the amount of GHG released into the atmosphere.

Simulated soil water distribution patterns and water use of Alfalfa under different subsurface drip irrigation depths

Alfalfa is one of the major perennial forage crops in California, vital for the livestock industry, and provides environmental benefits to the ecosystem in the state. Information on subsurface drip irrigation (SDI) practices on alfalfa is limited particularly in areas related to drip tape spacings and installation depths and their impacts on topsoil profile wetting patterns and alfalfa productivity. The objective of this study was to compare three different depths of drip lines: 15, 30, and 45 cm on topsoil profile wetting patterns and identify the optimum depth for achieving sustainable management practices for alfalfa production under SDI. Crop water requirements were determined using Tule Technologies system. Volumetric soil water contents from twelve cuts were simulated using HYDRUS-2D. Initial volumetric soil water contents from Watermark sensors were used in the model and measured volumetric soil water distributions were used for hydraulic conductivity calibration. Simulated results showed that there was no significant difference between root water uptake (RWU) among the various drip depths. RWU was 171.6, 170.0, and 168.2 cm at drip line depths of 15, 30, and 45 cm, respectively. Applied irrigation water during the study period was 195.1 cm while rainfall was 4.1 cm. A 10% reduction in topsoil volumetric soil water content was observed for drip lines at 30 cm depth as compared with 15 cm depth, while a 20% reduction in topsoil volumetric soil water content was observed for drip lines at 45 cm depth as compared with 15 cm depth. Drip lines at 30 cm depth are likely the optimal for RWU and free drainage; however, drip lines at 45 cm depth may allow growers to provide additional irrigation events (without increasing the topsoil volumetric soil water content) closer to the harvest date, potentially resulting in higher yield and water use efficiency.

Study on Modeling and Evaluating Alfalfa Yield and Optimal Water Use Efficiency in the Agro-Pastoral Ecotone of Northern China.

The agro-pastoral ecotone in northern China is the main production area of agriculture and animal husbandry, in which agricultural development relies entirely on groundwater. Due to the increasing water consumption of groundwater year by year, groundwater resources are becoming increasingly scarce. The substantial water demand and low germination rate in the first year are the main characteristics of alfalfa (Medicago sativa L.) yield in the agro-pastoral ecotone in northern China. Due to unscientific irrigation, water resources are seriously wasted, which restricts the development of local agriculture and animal husbandry. The study constructed the Dssat-Forages-Alfalfa model and used soil water content, leaf area index, and yield data collected with in situ observation experiments in 2022 and 2023 to calibrate and validate the parameters. The study found ARE < 10%, ENRMS < 15%, and R2 ≥ 0.85. The model simulation accuracy was acceptable. The study revealed that the water consumption at the surface soil layer (0-20 cm) was more than 6~12% and 13~31% than that at the 20-40 cm and 40-60 cm soil layers, respectively. The study showed when the irrigation quota was 30 mm, the annual yield of alfalfa (Medicago sativa L.) (7435 kg/ha) was consistent with that of the irrigation quota of 33 mm, and increased by 3.99% to 5.34% and 6.86% to 10.67% compared with that of irrigation quotas of 27 mm and 24 mm, respectively. To ensure the germination rate of alfalfa (Medicago sativa L.), it is recommended to control the initial soil water content at 0.8 θfc~1.0 θfc, with an irrigation quota of 30 mm, which was the best scheme for water-use efficiency and economic yield. The study aimed to provide technological support for the rational utilization of groundwater and the scientific improvement of alfalfa yield in the agro-pastoral ecotone in northern China.

Calibrating the STICS soil-crop model to explore the impact of agroforestry parklands on millet growth

ContextAgroforestry systems provide critical benefits for food security and climate change mitigation. Yet, they are complex and heteregoneous sytems hard to optimize. The use of process-based crop models provides an opportunity to understand better the interactions between soil, crop, tree and climate and explore the impact of agroforestry on crop growth, for contrasting crop management. ObjectiveThe objectives of this study were to i) calibrate the soil-crop STICS model for pearl millet (Pennisetum glaucum) in order to simulate millet potential growth and impact of water and nitrogen limitations on millet growth in open fields and ii) explore the impacts of the parkland tree Faidherbia albida on millet performance for contrasting N fertilizer inputs. MethodsWe gathered a comprehensive database of 28 agronomically contrasting situations, ranging from near-potential growth to drought- and N-stress, either on-station or in a farmer’s home- or bush-fields. Parameters governing relevant plant and soil processes for grain yield were calibrated in a stepwise procedure. The calibrated model was used to explore the impact on millet growth of the widely reported benefits of Faidherbia albida, namely a minimum reduction in radiation thanks to the peculiar reverse phenology of this tree, improvement of soil water content at the beginning of the growing season and of organic nitrogen in the topsoil. ResultsModel simulations with the calibration dataset were reasonably accurate for aboveground biomass and grain yield. Normalized Root Mean Square Errors (nRMSE) for these variables were 29% and 26%, respectively; model efficiency (EF) was 0.58 for both. The nRMSE ranged from 33% to 53% for Soil Water Content (SWC), plant N uptake, grain number, and leaf-area index (LAI). Model accuracy was lower with the evaluation dataset. In the virtual experiment, millet yield decreased with incoming solar radiation, but only at levels of shading (e.g. below 80% of the radiation obtained with full sun) that do not occur under Faidherbia. The decline was greater when millet was fertilized. Increasing the initial soil water content did not affect simulated millet growth. Simulated millet aboveground biomass and grain yield increased with higher organic nitrogen contents of the topsoil, by 80% when millet was not fertilizer, but only by 25% when millet was fertilized. ImplicationsThis study provides the first set of comprehensively calibrated parameters for applying STICS to pearl millet in open cropland. A virtual experiment with historical climate suggests that the benefits of Faidherbia decrease if farmers intensify crop production by adding more mineral N fertilizer. Hence, precise fertilizer management is recommended in Faidherbia parklands. These results illustrate the benefits of process-based crop modelling for better understanding the functioning of agroforestry systems.

The rainfall threshold of forest cover for regulating extreme floods in mountainous catchments

Floods frequently occur in mountainous regions and threaten lives and property worldwide. Forest cover usually plays an important role in regulating and preventing floods. However, the rainfall thresholds for forest cover to effectively regulate extreme flood are still unclear. In this study, we developed the topography-based subsurface storm flow hydrological (Top-SSF) model, which generally exhibited precise simulation performances in five typical mountainous catchments in southwest China. Then, the Top-SSF model was combined with a frequency analysis method to set different forest cover scenarios, investigating the relationship between rainfall threshold and forest cover in mountainous catchments. The results showed that under the control of soil saturated hydraulic conductivity (Ks) and maximum soil water storage capacity (Szm), the rainfall threshold of an extreme flood (the 100-year return period) increased significantly, especially when forest cover was larger than 70% of a catchment. Under the same forest cover, high initial soil water content (Swi) weakened the mitigating effect of forest cover on the extreme flood. In addition, a non-linear regression relationship between forest cover and rainfall threshold of a catchment was developed considering the impacts of Ks, Swi and annual mean precipitation (P¯) of the catchment. The significant impact of forest cover change on extreme floods was not only due to changing the amount of forest cover but also the soil properties. These results contribute to the understanding of the impact of forest cover changes on extreme floods and may provide valuable insights for flood defence in mountainous catchments.

Modeling the cooling effect of urban green spaces: The neglected control variables of ‘soil moisture’ and ‘biotope types’

Cooling by plant evapotranspiration (ET) is a prominent ecosystem service provided by urban green spaces (UGSs). UGSs counteract the warming of cities during heat waves. This study presents a GIS model to quantitatively assess the cooling intensity (CI) of UGS units (biotope types) during heat waves at the landscape scale. We conceptualize the CI as a physical index based on the ET of UGSs. Cooling intensities are calculated using the ambient temperature, biotope types, soil characteristics, and initial soil water conditions at the beginning of a heat wave as inputs. We calibrated and validated the model against the surface temperature in the city of Bochum, Germany, based on the thermal band of an orthorectified and calibrated atmospheric-, temperature- and emissivity-corrected mosaic from an airborne hyperspectral scanner. The Nash-Sutcliffe efficiency coefficient of the calibrated model is 0.75. The initial soil water content in the urban area affected the modeled CI by up to 2.6 K, and under the same transpiration rate, whether the initial ambient air temperature was 27 or 37 °C had effects of up to 2 K on the CI. The CI increased by up to 1 K with area size up to 2.5 ha. The purpose of the model was to evaluate and compare the CI of current and planned spatial patterns of land units to mitigate urban heat islands. The similar range of the goodness-of-fit criteria of the uncalibrated model compared to the calibrated model indicated the robustness and transferability of the model.

Soil water infiltration characteristics of reforested areas in the paleo-periglacial eastern Liaoning mountainous regions, China

Plantation forests (PF) and natural secondary forests (NSF) are the primary reforestation approaches. The establishment of PF can affect forest hydrological processes by changing soil structure. To date, few studies have focused on these changes and the effects on hydrological processes for the paleo-periglacial landform. To reveal reforestation approaches effects on water infiltration, including soil water infiltration capacity, retention capacity, and waterflow path pattern, we conducted field dye-tracer investigations with rainfall and laboratory infiltration experiments for the paleo-periglacial landform of eastern Liaoning mountains, China. The results showed that (1) Soil physical properties (including total porosity (TP), capillary porosity (CP), non-capillary porosity (NCP), initial soil water content (IWC), field water capacity (FWC)) and root abundance (RA) decreased with soil depth in both PF and NSF, while the soil bulk density (BD) and distribution of gravel content showed opposite changes. (2) Establishment of PF reduced the infiltration capacity and water retention capacity in the 0–20 cm layer, but enhanced the water retention capacity in 20–30 cm layer. Low IWC was conducive to increase soil water content (SWC) after infiltration. (3) Infiltration capacity parameters (including saturated hydraulic conductivity (Ks), SWC, difference between SWC and IWC (SWC–IWC), dye coverage ratio (DC)) were significantly correlated with BD, TP, CP, NCP, FWC, and fine roots RA (P < 0.05). Better connectivity gravels were more conducive to water infiltration. (4) Preferential flow was the main infiltration type, but with different waterflow paths pattern, with the 'funnel', 'finger' shape for PF, NSF, respectively. Increasing infiltration could increase flow path connectivity. Our findings show that soil physical properties, roots, and gravel occurrence affected soil infiltration, and different reforestation approaches had varying impacts on soil infiltration, water redistribution, transportation, and storage of surface and groundwater, improving the understanding of ecohydrological processes and effects of water resources management in forest ecosystems of paleo-periglacial landform.

Evaluating soil water movement and soil water content uniformity under sprinkler irrigation with different soil texture and irrigation uniformity using numerical simulation

Water movement and its distribution uniformity in the soil are essential for the design of sprinkler irrigation systems. They are both crucial factors influencing nutrient migration and the productivity of crops. In this study, a new numerical simulation method was proposed to investigate the soil water movement in sprinkler irrigation under nonuniform infiltration boundary conditions using COMSOL software. Besides, two soil tank experiments were conducted to test the reliability of the simulation model. Finally, the model was applied to evaluate the effects of sprinkler irrigation uniformity, soil texture, and initial soil water content on soil wetting patterns and soil water content uniformity. The results showed that the COMSOL-2D predictions of the vertical wetting fronts were in good agreement with the experimental data. The soil texture and initial soil water content influenced the soil wetting pattern and the risks of surface runoff and deep percolation in sprinkler irrigation systems. When the water application rate was 11.35 mm h−1 with an irrigation duration of 10 h, it was easy to cause surface runoff in silty clay loam while deep percolation in loamy sand. Additionally, when the initial soil water content is high, it should be better to avoid irrigation or cut down the irrigation duration to prevent percolation. The water within the soil was more uniformly distributed than that applied through a sprinkler irrigation system. The uniformity coefficient of soil water content distribution (CUs) increased from 87.75 % to 95.56 %, as the uniformity coefficient of sprinkler irrigation (CU) increased from 40.74 % to 82.41 %. Although a higher initial soil water content brought a higher soil CUs value, it also led to a higher risk of percolation. The experimental and simulation results indicated that the COMSOL-2D model could be used to accurately simulate soil water movement in sprinkler irrigation and determine the suitable operation mode of low-pressure sprinklers.

Effect of Different Irrigation Managements on Infiltration Equations and Their Coefficients

The main aim of this paper was to analyze the sensitivity of the five infiltration equations (Kostiakov, Kostiakov–Lewis, Philip, Horton and SCS) and their coefficients to various ponding depths and initial soil moisture under different irrigation managements. The treatments included three qualities of water (electrical conductivity = 6, 3 and 0.6 dS/m), two managements of irrigation (intermittent irrigation and daily irrigation) and three irrigation periods (100, 45 and 8 days). The HYDRUS-1D model was calibrated to simulate infiltration in various initial soil moistures and ponding depths. Evaluating the performance of infiltration equations showed that the Horton and Kostiakov–Lewis had better accuracy and Kostiakov and SCS had less accuracy than the other equations. The empirical coefficients of SCS and Kostiakov had the most and least sensitivities, respectively. Furthermore, Horton was the most sensitive equation, while SCS was the least sensitive one. The output parameters under daily management were the most sensitive to variations in infiltration coefficients, especially when the salinity and sodium contents of water and soil were higher. The results also showed that the effect of the initial soil moisture on the infiltration coefficient in high permeable soil (arising from daily management) was greater; but in low permeable soil (arising from intermittent management), the ponding depth was more effective. It is concluded that the infiltration equations (specifically the SCS equation) and their coefficients (specifically coefficient c) should be calibrated relative to the initial soil moisture, ponding depth, soil solution and water irrigation quality. Particularly in areas with high permeable soil (in the daily management), the calibration of the infiltration equation should be conducted with the initial soil moisture. In these areas, the irrigation period should be controlled. In areas with low permeable soil (in intermittent management), calibration should be carried out relative to the ponding depth. In these areas, the inflow rate should be controlled.

Effects of freeze-thaw cycling on the engineering properties of vegetation concrete

Vegetation concrete has been widely applied for the ecological restoration of bare steep slopes in short-term frozen and non-frozen soil regions in China. However, field experiments conducted in seasonally frozen soil regions have revealed decreases in the bulk density, nutrient content and vegetation coverage. This study aimed to clarify the evolution process and mechanism of the engineering properties of vegetation concrete under atmospheric freeze-thaw (F-T) test conditions. The physical, mechanical, and nutrient properties of vegetation concrete were investigated using six F-T cycles (0, 1, 2, 5, 10 and 20) and two initial soil water contents (18 and 22%). The results revealed decreases in the acoustic wave velocity and cohesive forces and an increase in the permeability coefficient of the vegetation concrete owing to F-T action. X-ray diffraction tests indicated that the decreased cohesive force was closely related to the overall decrease in the content of gelling hydration products in the vegetation concrete. Additionally, the contents of NH4+–N, PO43–P and K+ in the vegetation concrete increased, whereas that of NO3−–N decreased. The loss rates of these soluble nutrients increased, indicating that the nutrient retention capacity of the vegetation concrete had decreased. Specifically, the decreased nutrient retention capacity was mainly related to the disintegration and fragmentation of larger aggregates due to F-T action. This study provides theoretical support for future research on improving the anti-freezing capability of ecological slope protection substrates in seasonally frozen soil regions.

Influence of relative compaction and degree of saturation on the deformation characteristics of bentonite under freeze-thaw cycles

Bentonite, consisting of clay minerals of the montmorillonite group, has been widely used as an adsorbent and backfill material in nuclear waste disposal and groundwater remediation. It is challenging to use bentonite as a filling material in cold regions since bentonite is highly sensitive to thermal environmental changes, during which its bulk volume and microstructure change significantly. In this study, a series of one-dimensional and three-dimensional freeze-thaw tests were carried out within a closed system to investigate the influencing factors of the deformation of bentonite under freeze-thaw cycles. Results show that the initial soil water content greatly impacts bentonite's deformation during freeze-thaw cycles. For an initial higher degree of saturation (Sr), the expansion caused by the formation of ice lenses has a greater impact than the shrinkage induced by dehydration, ice-cementation, and so on. Conversely, bentonite tends to shrink at a lower degree of saturation during freezing. And the critical degree of saturation that determines bentonite's behavior of frost heave or frost shrinkage seems to be roughly 0.8. As the number of freeze-thaw cycles rises, initially uncompacted bentonite clay becomes more compacted, and initially compacted bentonite clay remains unchanged.

Optimization of Soil-Sludge Mixtures by Compaction for Potential Use in Mine Site Reclamation

Studies have indicated the potential of mixtures of silty soil and sludge produced by active treatment of acid mine drainage for use in covers with capillary barrier effects for mine site reclamation. Very high water contents of sludge in the settling pond could negatively affect the required hydrogeotechnical properties of soil sludge mixtures with high sludge contents. The challenge is then to determine the optimum wet sludge content of soil-sludge mixtures with air entry values (AEV) and/or saturated hydraulic conductivity (ksat) required for use in mine site reclamation covers. This paper presents a method to determine the optimum wet sludge content βopt for obtaining the maximum dry density of compacted soil-sludge mixtures. Two types of soil (S1 and S2) and two types of sludge (A and W) were tested. It was observed that βopt can be determined when the initial water content of the soil used in the mixture is lower than the optimum water content determined from the Proctor curve of the soil alone (10 wt% and 6 wt% for soils S1 and S2, respectively) and that βopt does not change with increasing initial soil water content. Optimum wet sludge contents found were low (≈15 wt% and ≈7 wt% for mixtures containing soils S1 and S2, respectively) for the test conditions, indicting a limited quantity of reusable sludge in the mixtures. For all mixtures, the water content corresponding to βopt was close to the optimum water content of the soil alone. Results of soil water retention and saturated hydraulic conductivity (ksat) tests conducted on selected optimized mixtures indicated that the mixtures based on soils S1 and S2 have air entry values higher than 20 kPa and would be suitable for use in the moisture retention layer of covers with capillary barrier effects, while soil S2 and the derived mixtures exhibited ksat &lt; 10−7 cm/s and would be potential materials for the low permeability layer in low saturated hydraulic conductivity covers.

Soil‐dependent β and γ shape parameters of the Haverkamp infiltration model for 3D infiltration flow

AbstractEstimating of soil sorptivity () and saturated hydraulic conductivity () parameters by field infiltration tests are widespread due to the ease of the experimental protocol and data treatment. The analytical equation proposed by Haverkamp et al. (1994) allows the modelling of the cumulative infiltration process, from which the hydraulic parameters can be estimated. This model depends on both initial and final values of the soil hydraulic conductivity, initial soil sorptivity, the volumetric water content increase () and two infiltration constants, the so‐called and parameters. However, to reduce the number of unknown variables when inverting experimental data, constant parameters such as and are usually prefixed to 0.6 and 0.75, respectively. In this study, the values of these constants are investigated using numerical infiltration curves for different soil types and initial soil water contents for the van Genuchten‐Mualem (vGM) soil hydraulic model. Our new approach considers the long‐time expansions of the Haverkamp model, the exact soil properties such as , and initial soil moisture to derive the value of the and parameters for each specific case. We then generated numerically cumulative infiltration curves using Hydrus‐3D software and fitted the long‐time expansions to derive the value of the and parameters. The results show that these parameters are influenced by the initial soil water content and the soil type. However, for initially dry soil conditions, some prefixed values can be proposed instead of the currently used values. If an accurate estimate of and is the case, then for coarse‐textured soils such as sand and loamy sand, we propose the use of 0.9 for both constants. For the remaining soils, the value of 0.75 can be retained for . For constant, 0.75 and 1.5 values can be considered for, intermediate permeable soils (sandy loam and loam) and low permeable soils (silty loam and silt), respectively. We clarify that the results are based on using the vGM model to describe the hydraulic functions of the soil and that the results may differ, and the assumptions may change for other models.